This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The renin angiotensin aldosterone system (RAAS) plays an important role in the progression of renal diseases. Blockade of this system has yielded beneficial results in retarding injury and progression in numerous intrinsic renal diseases. This system, as well as other common mechanisms of progression, operate in chronic allograft nephropathy (CAN). This project will investigate the role of the renin angiotensin aldosterone system (RAAS) in the development of chronic renal allograft nephropathy (CAN). The specific aim is to perform a 5 year randomized placebo controlled primary prevention trial in 150 patients to determine if the angiotensin II receptor blocker, Losartan, can slow or prevent corticol interstitial volume expansion and graft loss from CAN in kidney transplant recipients. The proposed study should provide both pathophysiologic rational and a practical test of therapy in a disease for which there are presently few treatment options. Participants will be admitted to the GCRC for their 5 year exit biopsy.